1. Field of the Invention
The present invention relates to a path detection method and a receiving device thereof used in a direct spread spectrum communication method receiver using DS-CDMA: Direct Sequence-Code Division Multiple Access.
2. Description of the Related Art
A conventional example of a receiving method which enables random access by packet data in a mobile communication system using a direct spread spectrum communication method is disclosed in Japanese Unexamined Patent Application, First Publication No. 11-252044, wherein the reception of burst signals at a receiver of a base station of a mobile communication system is described, with a plurality of mobile devices simultaneously making access requests to the wireless base station using a common spread code. In the reception of burst signals, because when a plurality of mobile stations send the same spread code they interfere with one another, it is difficult to strictly control the transmitting power of the mobile device and the base station and therefore the dispersion of the level received by the wireless base station increases, the delay profile used to detect the path of each mobile station is disrupted, and the path detection ability is degraded. An object of the present invention is to resolve these problems.
FIG. 10 shows a structural block diagram of a receiving system of a wireless base station of the same Japanese Unexamined Patent Application, First Publication No. 11-252044. In a mobile station 200, short codes having orthogonal properties, such as Gold code or Walsh code, are sequentially and repeatedly assigned a pilot signal PL so as to make identification by a plurality of pattern symbols possible, and each mobile device 200 accesses a base station 300 with a burst signal which has undergone spectrum spreading with a spread code for burst signals, and which functions as a PL pattern. In the wireless base station 300, the signal is received by an antenna 310 and the received signal is converted from analogue to digital with an AD converter 320, and then undergoes reverse spread in the spread code decoder 400 to acquire the signal data. A plurality of spread code decoders 400 corresponding with the spread code of the burst signal are provided.
A burst signal decoder will be described using a spread code A as an example. Firstly, a spread code generator 410 for generating the spread code A, and a PL searcher 420, a PL-RAKE synthesizer 460 and a PL data decoder 470 corresponding with the type of PL pattern are provided. The PL searcher 420 inputs the burst signal which has been received from the mobile station and digitally converted and the spread code A, and using the spread code A and the code string of the PL pattern, determines the correlation components of the search range (PL profile) by PL component in-phase addition, and detects the multi-path of each PL pattern of the received burst signal.
The PL-RAKE synthesizer 460 RAKE synthesizes and outputs the correlation components for the multi-path of each PL pattern. The PL data decoder 470 has the functions of decoding the signals corresponding with each RAKE generated and output PL pattern, extracting the mobile station identifier incorporated in the decoded signal, assigning a mobile station identification number and outputting the data.
Furthermore, a plurality of tracking sections 440 which receive input of the spread code A output by the spread code generator 410 and the burst signal received from the mobile station which has undergone digital conversion, and perform a tracking process for the indicated path (the process whereby minute variations in the reception path timing, which occur due to variations in the propagation delay of the signal between the mobile station and the wireless base station as a result of variations in the position of the mobile station, are tracked); a correlator 450 which receives input of the same spread code A output by the spread code generator 410 and the burst signal received from the mobile station which has undergone digital conversion, and obtains the correlation components of the input signal in accordance with the output of the corresponding tracking section 440; and a path controller 430 for controlling the path are provided.
The PL searcher 420 receives input of the spread code A output by the spread code generator 410 and the burst signal received from the mobile station which has undergone digital conversion, calculates the correlation components throughout the search range in spread code A and determines the profile, and detects the path candidacy of the received burst signal. The path controller 430 receives input of the path information output by the PL searcher 420, determines which paths should be tracked and instructs the tracking section 440. Furthermore, in accordance with the path information instructed to the tracking section 440, the path controller 430 also issues instructions for connecting PL-RAKE synthesizers 460 corresponding with the same PL pattern.
Furthermore, the path detection method described in “From the Fundamentals to the Application of CDMA Technology” by Takuro Sato H9 12–26 Realize Co. Ltd, pp 51–53 will be explained as conventional technology, with reference to FIG. 8.
An example of the structure of a conventional path detection method is shown in FIGS. 8 and 11. This conventional path detection method comprises a correlator 1, an in-phase adder 20 and an addition result temporary storage memory 1 (numeral 21 in FIG. 8) attached thereto, an electric power adder 23 and an addition result temporary storage memory 2 (numeral 22 in FIG. 8) attached thereto, and a path detection apparatus 6.
A conventional path detection method having this type of construction operates in the following manner. FIG. 9 shows a flow chart describing the operation of this conventional example (see also, FIG. 11 illustrating the path detection method according to conventional technology).
Firstly, after the CDMA method frequency modulated signal is converted to a baseband signal in the high-frequency receiver, a correlation process is performed in the correlator 1 for the input data sequence (S21 in FIG. 9). Specifically, correlation calculations of the input data sequence and the system sequence where the pilot symbol is spread by the spread code which is assigned to each user, are conducted for the window width for which path detection is performed. Correlation calculation is performed for every time slot. Here, the correlation value output from the correlator 1 is a vector quantity.
Next, an in-phase addition process (see, e.g., stage 2 in FIG. 11) is performed by the in-phase adder 20 (step S22). Specifically, the correlation values of the input vector quantities undergo the addition process (e.g., (a)+(b) in FIG. 11) as a vector quantity. A judgement is made as to whether or not the correlation value has been added x number of times (step S23), and in the case where x iterative additions (e.g., x=2 in FIG. 11) have been completed, the in-phase counter for counting the number of iterations of in-phase addition is reset, in preparation for the next in-phase addition cycle (step S25) (see, e.g., (c)+(d), (e)+(f) in FIG. 11). In addition, the addition results are converted to a scalar quantity electric power value (see, e.g., A1, A2, A3, A4 in FIG. 11) and output to the electric power adder 23 (see, e.g., stage 2 in FIG. 11). In the case where the number of addition iterations has not reached x times, the addition results are stored (step S24) in the addition result temporary storage memory 1 (numeral 21 in FIG. 8; this addition result temporary storage memory may also be referred to as “memory 1”), and the process returns to step S21.
Next, an electric power addition process (see, e.g., stage 3 in FIG. 11) is performed by the electric power adder 23 (step S26). Specifically, the input electric power value undergoes y addition iterations (e.g., (A1+A2) in FIG. 11), and a delay profile (e.g., I and II in FIG. 11) is prepared. Here, a judgement is made as to whether or not the electric power value has been added y number of times (step S27), and in the case where y addition iterations (e.g., y=2 in FIG. 11) have been completed, the electric power addition counter for counting the number of iterations of electric power addition is reset, in preparation for the next electric power addition cycle (step S29) (e.g., (A3+A4) in FIG. 11). In the case where the number of addition iterations has not reached y times, the addition results are stored (step S28) in the addition result temporary storage memory 2 (numeral 22 in FIG. 8; this addition result temporary storage memory may also be referred to as “memory 2”), and the process returns to step S21.
Finally, the path to be assigned to each finger (RAKE synthesizer) is determined by the path detection apparatus 6, using the delay profile (e.g., I and II in FIG. 11) prepared by the electric power adder 23 (steps S30, S31) (see, e.g., stage 4 of FIG. 11). Specifically, by performing threshold value processing (step S30) for the input delay profile (e.g., I and II in FIG. 11), highly accurate paths are extracted and assigned to each finger (step S31). Subsequently, a judgement is made as to whether or not the data to be received has finished (step S32), and if the data is not finished the process returns to step S21. If the data has finished, the path detection process awaits the reception of the next data.
However with this conventional technology, because the timing with which the in-phase adder and the electric power adder perform output to the next step in the process is limited by the total number of correlation values to be added, the number of times the path detection process is executed cannot be increased without decreasing the total number of correlation values (see, e.g., FIG. 11 illustrating that the path detection process is executed twice according to delay profiles I, II for the first eight correlation values (a), (b), (c), (d), (e), (f), (g) and (h)). Accordingly, this conventional technology is restricted in that the time spent on the path detection process becomes fixed, and the path detection process time cannot be compacted or accelerated as much as is possible.